There are many applications where UV light sources are used for treating liquids. Wallenius Water AB in Sweden has developed and is selling water treatment equipment having a water purifier comprising an elongated tubular treatment chamber with an inlet and an outlet. In the centre of the treatment chamber a generally tubular quartz glass is arranged and inside the quartz glass is a UV source arranged, such as a lamp capable of generating wavelengths in the UV region.
An important aspect of UV-light treatment is to ensure that as much liquid as possible is treated, i.e. exposed, to a predefined lowest UV-light treatment dose. Thus, it must be possible to guarantee that specified treatment requirements are fulfilled, e.g. that essentially a major part of the liquid receives a UV-dose that is above a predetermined UV-light treatment dose threshold.
One type of UV-light treatment reactor comprises an elongated UV-lamp arranged within a protective sleeve and provided with a circumferential channel outside the sleeve where the liquid is intended to flow. In the channel the liquid closest to the sleeve will receive the highest dose. And consequently the liquid farther out from the sleeve will receive a lower dose.
The treatment chamber may be considered to have different dose intensity zones. Closest to the UV-lamp is the dose intensity zone having the highest UV-light dose.
Micro-organisms are inactivated by UV light as a result of damage to nucleic acids. The high energy associated with short wavelength UV energy, primarily around 260 nm, is absorbed by cellular RNA and DNA. This absorption of UV energy forms new bonds between adjacent nucleotides, creating double bonds or dimers. Dimerization of adjacent molecules, particularly thymine, is the most common photochemical damage. Formation of numerous thymine dimers in the DNA of bacteria and viruses prevents replication and their ability to infect.
The germicidal effects of UV are directly related to the dose of UV energy absorbed by a micro-organism. The UV dose is the product of the UV intensity and the time that a micro-organism is exposed to UV light (often referred to as residence time). The required disinfection limit or log-reduction will dictate the required UV dose. UV dose is typically expressed in mJ/cm2, J/m2 or μWs/cm2. The exposure time of the UV system is determined by the reactor design and the flow rate of the water. The intensity is affected by the equipment parameters (such as lamp type, lamp arrangement, etc.) and water quality parameters (such as UV transmittance, etc.). Unlike chemical disinfectants, UV disinfection is not affected by the temperature, turbidity or pH of the water.
The UV dose response of a micro-organism is a measurement of its sensitivity to UV light and is unique to each micro-organism. A UV dose response curve is determined by irradiating water samples containing the micro-organism with various UV doses and measuring the concentration of viable infectious micro-organisms before and after exposure. The resultant dose response curve is a plot of the log inactivation of the organism versus the applied UV dose rate. 1-log inactivation corresponds to a 90% reduction; 2-log to a 99% reduction; 3-log to a 99.9% reduction and so on.
Thus, in order to achieve effective performance with regard to deactivation of micro-organisms, the reactor has to be designed to ascertain that also the liquid farther away from the UV-lamp receives the required dose, which may be achieved by increasing the UV radiation. However, this has a negative impact of the energy consumption of the UV-lamp, which will be high.
In the following some exemplary prior art will be discussed, that disclose various related aspects, and specifically devices where various types of mixing of the liquid is provided.
U.S. Pat. No. 6,224,759 relates to a UV system comprising UV lamp units intended to radiate UV-light to a liquid. By arranging ring-shaped devices, e.g. washers, on each lamp unit the turbulent mixing of the liquid is increased.
U.S. Pat. No. 6,420,715 relates to a method and an apparatus for improved mixing in fluids in a UV-light treatment system. The apparatus includes means, e.g. delta wings, specially shaped baffles, propellers or contoured flow tubes, for inducing vortices in the fluid flow through UV-light treatment system.
U.S. Pat. No. 7,385,204 relates to a fluid treatment device configured to treat a fluid with UV light. The device comprises a modular assembly including at least one baffle, e.g. a set of two baffles. The lamp geometry and baffles act as a baffling mechanism to direct the flow of fluid so as to increase uniformity in dose distribution by causing the fluid to flow into an area where it will receive uniform treatment.
U.S. Pat. No. 8,696,192 relates to an apparatus comprising non-planar baffles included in the flow such that a flow is permitted to pass the baffle in a gap between the inner peripheral edge and the outer surface of the UV-transparent inner tube. Thereby vortices are induced in the liquid flow with the intention to increase efficiency in UV-light treatment.
In US2011/0318237 is disclosed a UV reactor comprising a baffle having a helical shape to provide for radial mixing of liquid. In another variation segmented baffles are provided to achieve helical mixing.
And finally, US2013/0153514 relates to an apparatus for treating fluids using ultraviolet light. The disclosure is in particular directed to a treatment chamber having an elliptical cross-sectional shape, but also mixing aspects are discussed. A mixing device is provided within a UV-transmissive conduit comprising fixed or rotating fins in order to facilitate uniform rotational mixing throughout the length of the conduit, and thereby enhancing dosage uniformity.
Thus, the intention in many of the solutions presented herein is to achieve an enhanced radial mixing of the fluid in the treatment reactor in order to achieve a more uniform UV-light treatment dose. Various means are presented to achieve this object, e.g. “open solutions” are applied, i.e. where means, e.g. wings, are arranged to control the formation of helix-shaped liquid flows within a liquid enclosure.
The object of the present invention is to achieve an improved liquid treatment system with regard to an improved bacteria reduction in comparison to a conventional treatment device of today of a corresponding size. The system also improves the capabilities with regard to energy consumption and also with regard to decrease the adherence of fouling or scaling to the UV-transparent surfaces.